An absolute surface encoder employing a mode-locked femtosecond laser

An absolute surface encoder employing a mode-locked femtosecond is newly proposed. The encoder utilizes a variable line space (VLS) grating, whose grating pitch interval varies continuously with its grating position. When the femtosecond laser having a wide range light spectrum is illuminated onto the VLS grating, each wavelength diffracts with a difference diffraction angle. In addition, the diffraction angle of each wavelength changes corresponding to the position of the VLS grating due to the different grating pitch at each position. Therefore, it is possible to measure the absolute position by detecting the diffracted wavelengths by a detector with a designed angle. This paper reports about some basic verification about the feasibility of the proposed absolute surface encoder.